1. Field of the Invention
The present invention relates to an illumination apparatus, and more specifically to an illumination apparatus with high efficiency to allow a prescribed pattern to be formed efficiently even when a size of a light source is too large to be considered as a point source.
2. Description of the Background Art
Conventional illumination apparatuses have been formed as follows.
(a) Light emitted from a filament arranged in the vicinity of a focus of a paraboloid extends in all directions and is reflected on the paraboloid to form parallel rays. The parallel rays are formed into a desired light distribution pattern by a front lens (for example, see Japanese Patent Laying-Open Nos. 2002-50212 and 2002-50213).
(b) Light emitted from a filament is formed into a desired light distribution pattern by a multi-surface mirror and is then projected forward. A front lens only serves as a cover. The multi-surface mirror includes components each having a size and an angular arrangement as determined such that the component reflects the light entering from the filament into a prescribed direction and the combination of the components results in a desired light distribution pattern (see the patent specifications as listed above).
A desired light distribution pattern has been obtained efficiently using such illumination apparatuses.
Recently, high-power LEDs (Light Emitting Diode) have been commercially available to provide a light source with an extremely high luminosity. Such a high-power LED is large in size, and with a conventional light distribution structure of a illumination apparatus where a light source is regarded as a point source, a large amount of light emission thereof cannot be fully utilized. Therefore, the efficiency is inevitably reduced.
In particular, when reducing the size of illumination apparatuses is pursued, efficiency reduction caused by increased disorder of light distribution is more likely to be brought about. A light source is arranged, for example, in the vicinity of a focus of a reflecting mirror of an illumination apparatus. When the reflecting mirror is reduced in size with its focal length reduced, the light, for example, from a location shifted from the focus of the filament does not radiate as intended, resulting in disorder of light distribution and reduced efficiency. In other words, even if the light source is of the same size, miniaturization increases the influence of displacement at the location shifted from the focus of the light source and increase the disorder of light distribution. Therefore, the valuable high-power LED cannot be used efficiently.